RMAN备份优化(Backup Optimiz…

RMAN备份优化(Backup Optimization)

RMAN中的备份优化(Backup
Optimization)是指在备份过程中，如果满足特定条件，RMAN将自动跳过某些文件而不将它们包含在备份集中以节省时间和空间。

说的直白些就是能不备的它就不备了，不像原来甭管文件有没有备份过统统再备一遍。

通常必须满足如下几个条件的情况下，才能够启用备份优化的功能：

(1).CONFIGURE BACKUP OPTIMIZATION参数置为on；

(2).执行的BACKUP DATABASE或BACKUP ARCHIVELOG命令中带有ALL或LIKE参数。

(3).分配的通道仅使用了一种设备类型，也就是没有同时分配使用sbt与disk的多个通道。

打开备份优化设置通过如下命令：

RMAN> CONFIGURE BACKUP OPTIMIZATION ON;

那么在进行备份优化时，RMAN是如何判断要备份的文件是否需要被优化呢，这个算法就相当复杂了，而且可能影响优化算法的因素也非常多，假如某库在上午9点被执行过一次全库备份，等下午3点再次执行全库备份时，备份的文件没有变动而且也已经被备份过时，才会跳过这部分文件。所以理论上备份优化仅对于只读表空间或offline表空间起作用。当然对于已经备份过的archivelog文件，它也会跳过。
http://blog.sina.com.cn/s/blog_63a2aa330100nata.html
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下为OCP试题

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115. You set the recovery window to seven days and the backup optimization to ON using the

CONFIGURE command of Recovery Manager (RMAN). The most recent backup of the TOOLS

tablespace to disk was taken on January 3. The TOOLS tablespace is read­only.

On February 21, when you execute a command to back up all the tablespaces to disk, you find that RMAN

backs up the TOOLS tablespace also, even though the contents of the tablespace have not changed after

the backup on January 3.

Because there are no changes made to the TOOLS tablespace, you decide that the tablespace should

not be backed up by RMAN. What can you to do skip backing up the TOOLS tablespace without changing

the current backup optimization setting?

A.configure a default device for RMAN backups

B.temporarily disable the retention policy for RMAN backups

C.configure automatic channel allocation for RMAN backups

D.use the CONFIGURE command to reconfigure the recovery window to 60 days

Answer: B